Often, it is desired to detect a characteristic of a product undergoing heating so that action with respect to the heated product may be taken. For example, it may be necessary to detect when a product undergoing cooking has reached a desired doneness so that the source of heat for the cooking process can be deactuated. One known apparatus comprises a toaster which typically detects the temperature near a surface of piece of bread to determine when the bread has been toasted to a desired doneness. However, it has been found that the temperature near the surface of a product undergoing cooking can be a poor indicator of doneness.
In view of the foregoing difficulty, and/or where other products are to undergo heating, it may prove desirable to sense one or more additional or alternative characteristics, for example food surface color change, exhaust air odor change, onset of steaming, boiling rate and/or sizzling sounds. The need to sense product doneness is particularly important in high power cooking devices, such as a high speed light oven. Typically, such an oven is controlled by an operator, who visually observes the product undergoing heating and, when the desired brownness of the food product is detected, the food item is removed from the oven or the oven is shut off. However, in a high speed light oven, brownness is not easily detected due to the extremely high intensity of light present in the cooking cavity causing everything to appear white hot. The ability of an operator to detect surface brownness is thus impaired, thereby leading to poor or even disastrous cooking results, such as undercooking, overcooking, boil-over and possible blackening and ignition of the food product. Because of the foregoing problems, automatic control is highly desirable if not essential, especially for commercial cooking products where menu items must be cooked consistently in high volume day after day.